Preliminary investigation showed the murder was a "preplanned terrorist act by Quetta Shura", Shafiqullah Tahiri, a National Director of Security (NDS) official, told a press conference in Kabul.

He quoted Peace Council member Rahmatullah Wahidyar as saying that Hamidullah Akhund, representing the Quetta Shura, maintained constant contact with the panel over the last four months.

"The man said he had positive messages for the peace council and wanted to share them with you," he added. Hamidullah repeatedly came to Kabul to visit council leadership and returned to Quetta for final results.

Unable to travel to Afghanistan frequently, Hamidullah was later replaced by Esmatullah, Tahiri added.

HPC Secretary Masoom Stanikzai and Wahidyar were in picture on Esmatullah's latest visit to Afghanistan, the official said. The issue is being investigated to ascertain who else was involved in the incident.

Esmatullah stayed in an HPC guesthouse for a few nights, according to Tahiri, who said the courier claimed to have brought fresh messages for the peace council.

Also present at the news conference, Wahidyar confirmed the details provided by the NDS official. "We went to Ustad Rabbani's home in Wazir Akbar Khan at 5:40pm on Tuesday.

"After security checks, we were let in. The explosion happened as soon as the militant embraced Rabbani. His martyrdom is an irreparable loss and a huge blow to the peace process for Afghanistan."